Vascular headache syndromes such as migraine are among the most common of all medical problems. However, the neural basis of vascular headache is poorly understood and highly controversial. Current research on the mechanisms of vascular headache has focused on the role of a pain- sensitive sensory innervation of cranial blood vessels that arises from the trigeminal nerve. Further understanding of the role of this sensory pathway in vascular head pain is limited by critical gaps in our knowledge of those properties of the pathway that relate specifically to its sensory function and the transmission of nociceptive information. In order to better understand the peripheral mechanisms of vascular head pain, the proposed studies will characterize the physiological properties of primary afferent neurons that innervate the major blood vessels of the intracranial dura. Single-unit recording will be used to study the discharge activity of dural primary afferent neurons during graded mechanical, thermal, and chemical vascular stimulation in anesthetized rats. Repeated stimulation paradigms will be carried out to investigate sensitization induced by different forms of vascular stimulation. The information provided by these studies will be critical for further progress in understanding the neural basis of vascular head pain.